Integration of Light Rail on the I-90 Floating Bridge across Lake Washington

Abstract

Installing light rail transit across a floating roadway bridge presents many unique challenges, foremost of which is how to design the multidimensional moving joints at both ends of transition spans between the fixed and floating structures. A technical solution to this technical challenge has been proposed, analyzed, modeled, designed, and prototype tested in the context of the East Link Extension, a light rail transit project being carried out by Central Puget Sound Regional Transit Authority (Sound Transit). Described are the planning, execution, and results of a full-scale prototype testing program of the proposed Curved Element Supported Rail (CESuRa) Track Bridge System, based on the relationship of curved rail supports in two independent planes that adjust in response to the movements of the Interstate 90 (I-90) Bridge. The prototype CESuRa track bridges performed as expected; the information gathered and lessons learned will greatly benefit the final design, the production track-bridge fabrication, and the installation process. Also discussed is the anticipated performance of these track bridges on the I-90 structure in conjunction with the proposed direct fixation track system, fixed rail anchors, and sliding rail expansion joints to be strategically located across the 1.1-mi I-90 Bridge. Built in 1989, the I-90 Bridge is the fifth-longest floating bridge in the world and carries three westbound and two reversible lanes of traffic between Seattle and Mercer Island, Washington. The bridge will be reconfigured to carry four westbound lanes, and the reversible lanes will be converted to light rail transit.

The CESuRa System: Allowing Changes in a Rail Track Profile While Maintaining Full Vertical Support

“…They were configured in various combinations of pitch, roll, and yaw, and trains were run over them at design speeds in order to investigate the dynamic response. The results demonstrated that the system performed as desired in terms of rider comfort and safety and that the geometric concepts underlying the accommodation of pitch functioned as intended [16,17].…”

“…Then, two complete track bridges were tested at the fabrication facilities of Jesse Engineering, in Tacoma, WA, USA, after they had been constructed, to verify that the complete system would behave as planned, particularly in view of the tight tolerance requirements that were identified during the first phase of testing. Last, the fabricated track bridges were shipped as complete units to Pueblo, CO, USA, where they were installed in the test track at the Transportation Technology Center [16,17]. They were configured in various combinations of pitch, roll, and yaw, and trains were run over them at design speeds in order to investigate the dynamic response.…”

“…The floating bridge project included evaluation of the CESuRa system using numerical simulations [13], preliminary proof-of-concept tests at the University of Washington [14,15], and full-scale tests of the system under dynamic LRV loads [16,17]. These studies showed that the system could accommodate joint rotations in excess of the project requirements with LRV travel at 88.5 kph (55 mph) [16].…”

“…These studies showed that the system could accommodate joint rotations in excess of the project requirements with LRV travel at 88.5 kph (55 mph) [16]. Stresses in the rails and bearer bars were found to be less than 138 MPa (20 ksi) under these conditions [14,17], the lateral displacements under LRV loading were less than 6 mm (0.25 in.) [17], and the vertical and lateral accelerations were found to be well within acceptable limits [13,16,17].…”

“…Stresses in the rails and bearer bars were found to be less than 138 MPa (20 ksi) under these conditions [14,17], the lateral displacements under LRV loading were less than 6 mm (0.25 in.) [17], and the vertical and lateral accelerations were found to be well within acceptable limits [13,16,17]. These studies investigated one potential geometry of a CESuRa system and showed that it could meet the project requirements.…”